Exploring the low-temperature oxidation chemistry of 1-butene and i-butene triggered by dimethyl ether

The low-temperature oxidation chemistry of alkenes, 1-butene, and i-butene oxidation experiments triggered by dimethyl ether (DME) were studied in a jet-stirred reactor at 790 Torr, 500 K–725 K and the equivalence ratio of 0.35. Low-temperature oxidation intermediates involved in alcoholic radical chemistry and allylic radical chemistry were detected using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). To better interpret the experimental data, a kinetic model was proposed based on low-temperature oxidation model of DME and comprehensive oxidation models of 1-butene and i-butene in literature. Based on present experimental results and modeling analysis, alcoholic radical chemistry initiated by OH addition is mainly responsible for the low-temperature chain propagation of butenes, since the Waddington mechanism plays a dominant role compared with the chain-branching pathways through the second O₂ addition. Allylic radical + HO₂. reactions producing alkenyl hydroperoxides and fuel + O₂ served as the major chain-branching and chain-termination pathways, respectively, and they were competitive in the negative temperature coefficient region. Meanwhile, chain-branching pathways originating from allylic radical + O₂ and alkyl-like radical + O₂ reactions had little contribution to the OH formation. Comparison with the simulation results of butane/DME mixtures demonstrated that butenes could largely inhibit the reactivity of DME at low temperatures due to its reduced low-temperature chain-branching process.